Elevator driving system

ABSTRACT

An elevator driving system comprising a three-phase induction motor including three-phase armature windings having a plurality of terminals and arranged for change-over between the double star connection mode and the delta connection mode, means for connecting said armature windings in the double star connection mode to a three-phase a.c. power supply when the elevator is driven for service operation, means for connecting said armature windings in the delta connection mode to the three-phase a.c. power supply when the elevator car is driven for maintenance operation, means for changing over the connection mode of said armature windings to the delta connection during application of the brake, and a controlled rectifier circuit for applying a d.c. voltage across selected two terminals among said terminals during the same braking period.

United States Patent 1191 Mitsui et al.

145] Jan. 14, 1975 ELEVATOR DRIVING SYSTEM Primary ExaminerRobert K.Schaefer [75] Inventors: Nobuo Mitsui, Katsuta; Tadao Ass'stam Exammerw' Dupcanson Kameyama Higashi; Akinori Attorney, Agent, or Fzrm-Cra1g &Antonelli Watanabe, lbaraki; lsao Fukushima; Takanobu Hatakeyama, bothof [57] ABSTRACT Katsuta, n f Japan An elevator dr1v1ng system comprlsmga three-phase induction motor including three-phase armature wind- [73]Asslgnee: Tokyo Japan ings having a plurality of terminals and arrangedfor 22 Filed; May 29, 1973 change-over between the double starconnection mode and the delta connection mode, means for con- [2]] Appl'364,494 meeting said armature windings in the double star connectionmode to a three-phase ac. power supply when 52 U.S. c1. 187/29 R,318/226 the elevator is driven for Service Operation means for [51]IntfCl. H02k 7/48 Connecting Said armature windings in the delta [58]Field of Search 187/29; 318/212, 225, 226, nection mode to thethree-Phase power pp y 313 373 377 37 323 20 75 when the elevator car isdriven for maintenance operation, means for changing over the connectionmode 5 References Cited of said armature windings to the deltaconnection dur- UNITED STATES PATENTS ing application of the brake, anda controlled rectifier circuit for applying a dc. voltage acrossselected two E253 Q terminals among said terminals during the same brak-3,414,774 12/1968 Motta 323/20 x mg Perlod' 18 Claims, 8 Drawing FiguresK i V -o -O W SI 82:: 83::

Pl P2 P3 1: $131 SR 2 P217, 'PiQ i u U 1, S Ul lvz\w| SCR2 PATENTED I3860.093

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PATENTED 4 3.860.093

sum anr 4' ELEVATOR DRIVING SYSTEM This invention relates toimprovements in elevator driving systems, and more particularly toimprovements in the elevator driving system in which the driving sourceis a three-phase induction motor.

Three-phase induction motors which are inexpensive are generallyemployed as a driving source for common-type elevators.

Elevator cars are driven at different operating speeds depending on thenormal operation for carrying passengers and freight (hereinafterreferred to as service operation) and the special operation for thepurpose of maintenance or repair works (hereinafter referred to asmaintenance operation). During the service operation, the speed of theelevator car is desirably as high as possible so as to improve theefficiency of transportation. On the other hand, during the maintenanceoperation, maintenance engineers work frequently on the roof of theelevator car, and therefore, the work will be attended with dangerunless the elevator car is driven at a low speed. Thus, the drivingsource for the elevator car must be capable of realizing these twodifferent speeds.

It is very difficult for a conventional three-phase induction motor tooperate at both such high and low speeds. It is thus common practice toprepare two sets of armature windings in an induction motor for anelevator car so that one of the two sets of armature windings can beused for the service operation and the other set can be used for themaintenance operation. Further, during the service operation, thelow-speed winding set is energized frequently for several secondsimmediately before the stoppage of the elevator car at the target floorso that the elevator car can be stopped at the target floor withimproved accuracy.

In the driving source having two sets of armature windings as abovedescribed, the number of poles is determined depending on the speed forservice operation and the speed for maintenance operation. However, theinduction motor having these two sets of armature windings is naturallybulky and expensive compared with common induction motors.

It is therefore an object of the present invention to provide anelevator driving system employing an induction motor which is relativelysmall in size and inexpensrve.

Another object of the present invention is to provide an elevatordriving system which can produce a sufficiently large braking torquethereby facilitating the control of an elevator car.

A first feature of the present invention resides in the fact that theelevator driving system comprises a threephase induction motor includingthree-phase armature windings each having an intermediate terminal andar-' ranged for change-over between the double star connection mode andthe delta connection mode, means for connecting the intermediateterminals of the respective phase windings to a three-phase a.c. powersupply so that the connection mode of said armature windings can bechanged over from the delta connection mode to the double starconnection mode when the elevator car is driven for service operation,and means for connecting the apex terminals (terminals at apexes of thedelta or triangle) of the delta connection to the three-phase a.c. powersupply when the elevator car is driven for maintenance operation.

' A second feature of the present invention resides in the fact that theelevator driving system comprises further means for applying a dc.voltage across two terminals selected from a group consisting of saidapex terminals and said intermediate terminals while maintaining saidarmature windings in the delta connection mode when a brake is appliedto the elevator car.

Other objects, features and advantages of the present invention will beapparent from the following detailed description ofa preferredembodiment thereof taken in conjunction with the accompanying drawing,in which:

FIG. 1 is a diagrammatic view showing the structure of an embodiment ofthe elevator driving system according to the present invention;

FIG. 2 is a connection diagram of the induction motor shown in FIG. 1when the elevator car is started and accelerated for service operation;

FIG. 3 is a connection diagram of the induction motor when the elevatorcar is driven for maintenance operation;

FIGS. 4A to 4D are connection diagrams of the induction motor when abrake is applied to the elevator car; and

FIG. 5 is, a graph showing the relation between the number ofrevolutions of the induction motor and the braking torque.

Referring now to FIG. 1, a three-phase a.c. power supply generallydesignated by U, V and W supplies power to an induction motor IM througha main switch K. This induction motor IM is desirably of thesquirrelcage type although the armature windings thereof are merelyshown in FIG. 1. In FIG. 1, the armature windings are shown connected inthe delta connection mode and have six terminals. More precisely, thearmature windings include three intermediate terminals U V and W in therespective phases in addition to the apex terminals U V and W of thedelta connection. It is apparent that the connection mode of theinduction motor having such armature windings and terminals can bechanged over between the double star connection and the deltaconnection. Contactors P P P Pxl, Px2 and S S 8;; are provided forcarrying out such change-over.

When the contactors P P P and Pxl, Px2 are closed, the intermediateterminals U V and W are connected to the three-phase a.c. power supplyterminals U, V and W, and theapex terminals U V, and W, are connected toeach other as seen in FIG. 2 so that the three-phase induction motor IMoperates with the double star connection mode. On the other hand, whenthe contactors S S and S are closed, the apex terminals U,, V, and W ofthe delta connection are connected directly to the three-phase a.c.power supply terminals U, V and W as seen in FIG. 3 so that thethree-phase induction motor IM operates now with the delta connectionmode.

The number of poles in the double star connection mode differs from thatin the delta connection mode, and the former is one-half of the latter.Therefore, when the number of poles in the former connection mode isfour, the number of poles in the latter connection mode is eight, andthe rotating speed of the induction motor in the former case is twicethat in the latter case. It will thus be understood that a two-speedmotor can be obtained by the provision of only one set of armaturewindings whose connection mode can be changed over in the manner abovedescribed, and an undesirable increase in the size of the motorresulting in a high cost can be avoided.

An electromagnetic brake MB, a tachometer generator TG and a sheave SHare operatively connected to the rotor of the induction motor IM. Thesheave SH causes vertical movement of an elevator can CA and acounterweight CW through a rope RP.

In starting the elevator car CA for service operation, the contactorsP,, P P and Pxl, Px2 are closed and a notch control means (not shown) isactuated for accelerating the elevator 'car CA. A braking torque must beapplied to the accelerated elevator car CA in order to stop the elevatorcar CA at the target floor. A large braking torque is requiredespecially when the elevator car CA is moving upward with a full load ordownward with a light or no load. Such a braking torque is produced inthe induction motor and d.c. braking is generally employed for thispurpose. However, due to the fact that the induction motor IM isoperated with a connection mode as shown in FIG. 2, a sufficiently largebraking torque cannot be obtained even when d.c. braking is applied tothe induction motor in the state shown in FIG. 2. In order to obtainsuch a braking torque, the contactors Pxl and Px2 are opened todisconnect the apex terminals U,, V, and W, from each other, and afterrestoring the connection mode from the double star connection to thedelta connection, a d.c. voltage is applied across the properly selectedtwo terminals of the armature windings.

This d.c. voltage is obtained by a controlled rectifier circuit REconnected across the two terminalsU and V of the ac power'supply. Therectifier circuit RE is a bridge circuit composed of thyristors SCR,,SCR, and

, diodes SR,, SR At the time at which the brake should be applied,contactors B, and B, are closed to turn on the thyristors SCR, and SCRso as to produce a braking force corresponding to the firing angle. Therectitier circuit RE may be a bridge circuit composed of fourthyristors, but it is preferable to include the diodes SR, and SR, inthe arms thereof as shown in FIG. 1. Such an arrangement is advantageousin that it includes a route which can continuously supply brakingcurrent to the motor in the forward direction when viewed from the d.c.side of the rectifier circuit. Thus, a smooth braking torque can beobtained by the flywheel effect such that the direct current for brakingcan be continuously supplied in spite of on-off of the input current atthe ac. side. In this case, the d.c. braking is controlled by anelectric circuit as shown in FIG. 4A in which the intermediate terminalsU and V, of the armature windings are connected across the rectifiercircuit RE.

In the elevator system, the d.c. braking is generally controlled bycomparing the instructed speed with the actual speed of the elevator carCA. It is desirable to generate a suitable speed instruction signal fordecelerating the elevator car CA depending on the result of detection ofthe physical position of the elevator car CA in order to improve theaccuracy with which the elevator car CA arrives at the target floor.This position detecting device comprises a position detector PT mountedto the elevator car CA and a plurality of detecting elements PP disposedin the shaft. The output of these detecting elements PP is applied to aspeed instruction signal generator SP which generates a speedinstruction signal depending on the physical position of the elevatorcar CA. This speed instruction signal is compared with the output of thetachometer generator TG in a comparator CM and the error therebetween isapplied from the comparator CM to an automatic pulse phase shifter PSwhich .controls the turn-on of the thyristors SCR, and SCR As theelevator car CA which is decelerated by the speed instruction signalapproaches a point in close proximity to the target floor, theelectromagnetic brake MG is energized by the output of the positiondetecting element PP so as to stop the elevator car CA at the targetfloor. In this manner, the elevator car CA can be smoothly and reliablystopped at the target floor, and yet, the accuracy of floor arrival isquite high so that the elevator car CA can bestopped within the range oft 10 mm from the target floor level.

The above description has referred to the case in which the d.c. voltageis applied across the intermediate terminals U and V, of the armaturewindings of the induction motor IM whose connection mode is changed overfrom the double star to the delta connection. However, a sufficientlylarge braking torque can be similarly obtained by applying such d.c.voltage across any other selected terminals when the connection mode ofthe armature windings is changed over from the double star to the deltaconnection.

Referring to FIG. 1 again, the contactors B, and B connected at oneterminal thereof to the d.c. terminals of the rectifier circuit RE maybe connected at the other terminal thereof to the terminal of thearmature windings different from those above described. It has beenalready described that FIG. 4A represents an electric circuit in whichthe contactors B, and B are connected at the other terminal thereof tothe two in tertnediate terminals U and V of the armature windingsrespectively.

FIG. 4B shows an electric circuit in which the contactors B, and B areconnected at the other terminal thereof to the apex terminals U, and V,respectively of the armature windings for applying d.c. braking. ln thiscase too, a braking torque which is substantially equal to thatdescribed with reference to FIG. 4A can be obtained.

FIG. 4C shows another electric circuit in which the contactors B and, B,are connected at the other terminal thereof to the apex terminal V,among the apex terminals u,, V, and W, of the armature windings and tothe intermediate terminal V disposed opposite to the apex terminal V,respectively for applying d.c. braking. In this case, the. brakingtorque is less than those described with reference to FIGS. 4A and 4B,but this arrangement is effective in that the temperature rise of thearmature windings can be uniformalized due to the fact that. currentflows uniformly'through all the portions of the armature windings.

FIG. 4D shows another electric circuit in which the contactors B, and Bare connected at the other terminal thereof to the apex terminal U,among the apex ter' minals U,, V, and W, of the armature windings and tothe intermediate terminal U, adjacent to the terminal U, respectivelyfor applying d.c. braking. This arrangement is not sosatisfactory due tothe fact that the braking torque is less than that obtained with thearrangement shown in FIG. 4C. However, the braking torque is more thanwhen d.c. braking is applied in the state of the double star connection.

FIG. 5 is a graphic representation of the result of comparison betweenthe values of the d.c. braking troque. It will be seen from FIG. 5 thatthe value of the braking torque is quite small when dc. voltage isapplied across the terminals U and V in the state in which thecontactors Pxl and Px2 are closed and the armature windings remain inthe double star connection mode. A large braking torque can be obtainedwhen d.c..braking is applied in the state in which the contactors Pxland Px2 are opened to change over the connection mode from the doublestar to the delta connection. It will be seen that the value of thetorque is maximum especially when dc. voltage is applied across theterminals U and V or U and V What we claim is:

1. An elevator driving system comprising:

a three-phase induction motor including deltaconnected armature windingsand having apex terminals (U V,, W,) of the delta-connection andintermediate terminals (U V W of the respective phase windings;

means for connecting said apex terminals to one another and forsimultaneously connecting said intermediate terminals to a three-phasea.c. power supply for driving the elevator at a high speed; and

means for disconnecting the mutual connection of said apex terminal andfor simultaneously applying a dc. voltage across two terminalsarbitrarily selected from at least one of said apex terminals and saidintermediate terminals for braking the elevator.

2. An elevator driving system as claimed in claim 1 wherein said dc.voltage applying means comprises an a.c. power supply and a controlledrectifier circuit connected to said power supply and including aplurality of thyristors.

3. An elevator driving system as claimed in claim 2, wherein saidcontrolled rectifier circuit includes a route which can continuouslysupply direct current in the forward direction.

4. An elevator driving system as claimed in claim 2, further comprisingmeans for generating a speed instruction signal during application ofthe brake, means for detecting the rotating speed of said inductionmotor, means for comparing said speed instruction signal with thedetected speed of said induction motor, and means for controlling saidthyristors in response to the output of said comparing means.

5. An elevator driving system as claimed in claim 4, wherein means fordetecting the physical position of the elevator car is further provided,and said speed instruction signal generating means responds to theoutput of said position detectingmeans.

6. An elevator driving system according to claim 1, wherein said meansfor disconnecting and for applying a d.c. voltage applies the dc.voltage across two terminals arbitrarily selected from said apexterminals for braking the elevator.

7. An elevator driving system according to claim 1, wherein said meansfor disconnecting and for applying a dc. voltage applies the dc. voltageacross two terminals arbitrarily selected from said intermediateterminals for braking the elevator.

8. An elevator driving system according to claim 1, wherein said meansfor disconnecting and for applying a dc. voltage applies the dc. voltagebetween an arbitrarily selected apex terminal and an intermediateterminal of the phase winding opposite the selected apex terminal forbraking the elevator.

9. An elevator driving system according to claim 1, further comprisingmeans for connecting said apex terminals to a three-phase a.c. powersupply for driving the elevator at a high speed.

10. In an elevator driving system in which the elevator is driven by athree-phase induction motor at different speeds, and a control system isprovided for the motor, the improvement comprising the three-phaseinduction motor having delta-connected armature windings, apex terminalsfor the delta-cconnection and intermediate terminals for the respectivephase windings, the control system for the motor including means forconnecting said apex terminals to one another and for simultaneouslyconnecting said intermediate terminals to a three-phase a.c. powersupply for driving the elevator at a high speed, and means fordisconnecting the mutual connection of said apex terminals and forsimultaneously applying a dc. voltage across two terminals selected fromat least one of said apex terminals and said intermediate terminals forbraking the elevator.

11. In an elevator driving system according to claim 10, the controlsystem further including means for connecting said apex terminals to athree-phase a.c. power supply for driving the elevator at a low speed.

12. A method for driving an elevator in which a three-phase inductionmotor having delta-connected armature windings, apex terminals of thedeltaconnection and intermediate terminals of the respective phasewindings is provided, the method comprising the steps of connecting theapex terminals to one another and simultaneously connecting theintermediate terminals to a three-phase a.c. power supply for drivingthe elevator at a high speed, and disconnecting the mutual connection ofthe apex terminals and simultaneously applying a dc. voltage across twoterminals selected from at least one of the apex terminals and theintermediate terminals for braking operation of the elevator.

13. A method according to claim 12, wherein the step of disconnectingand applying a dc. voltage includes applying the voltage across twoterminals selected from the apex terminals or braking operation of theelevator.

14. A method according to claim 12, wherein the step of disconnectingand applying a dc. voltage includes applying the voltage across twoterminals selected from the intermediate terminals for braking operationof the elevator.

15. A method according to claim 12, wherein the step of disconnectingand applying a dc. voltage includes applying the voltage between anarbitrarily selected apex terminal and an intermediate terminal of thephase winding opposite to the selected apex terminal for brakingoperation of the elevator.

16. A method according to claim 12, wherein the step of disconnectingand applying a dc. voltage includes applying the voltage via acontrolled rectifier circuit having a plurality of thyristors andconnected an an a.c. power supply.

17. A method according to claim 16, further comprising the steps ofgenerating a speed instruction signal during braking operation of theelevator, detecting the rotating speed of the induction motor, comparingthe speed instruction signal with the detected speed of the inductionmotor, and controlling the thyristors in response to the result of thecomparison.

18. A method according to claim 17, further comprising the steps ofdetecting the physical position of the elevator car and controlling thegeneration of the speed instruction signal in accordance with thedetected position of the elevator car.

1. An elevator driving system comprising: a three-phase induction motorincluding delta-connected armature windings and having apex terminals(U1, V1, W1) of the deltaconnection and intermediate terminals (U2, V2,W2) of the respective phase windings; means for connecting said apexterminals to one another and for simultaneously connecting saidintermediate terminals to a three-phase a.c. power supply for drivingthe elevator at a high speed; and means for disconnecting the mutualconnection of said apex terminal and for simultaneously applying a d.c.voltage across two terminals arbitrarily selected from at least one ofsaid apex terminals and said intermediate terminals for braking theelevator.
 2. An elevator driving system as claimed in claim 1 whereinsaid d.c. voltage applying means comprises an a.c. power supply and acontrolled rectifier circuit connected to said power supply andincluding a plurality of thyristors.
 3. An elevator driving system asclaimed in claim 2, wherein said controlled rectifier circuit includes aroute which can continuously supply direct current in the forwarddirection.
 4. An elevator driving system as claimed in claim 2, furthercomprising means for generating a speed instruction signal duringapplication of the brake, means for detecting the rotating speed of saidinduction motor, means for comparing said speed instruction signal withthe detected speed of said induction motor, and means for controllingsaid thyristors in response to the output of said comparing means.
 5. Anelevator driving system as claimed in claim 4, wherein means fordetecting the physical position of the elevator car is further provided,and said speed instruction signal generating means responds to theoutput of said position detecting means.
 6. An elevator driving systemaccording to claim 1, wherein said means for disconnecting and forapplying a d.c. voltage applies the d.c. voltage across two terminalsarbitrarily selected from said apex terminals for braking the elevator.7. An elevator driving system according to claim 1, wherein said meansfor disconnecting and for applying a d.c. voltage applies the d.c.voltage across two terminals arbitrarily selected from said intermediateterminals for braking the elevator.
 8. An elevator driving systemaccording to claim 1, wherein said means for disconnecting and forapplying a d.c. voltage applies the d.c. voltage between an arbitrarilyselected apex terminal and an intermediate terminal of the phase windingopposite the selected apex terminal for braking the elevator.
 9. Anelevator driving system according to claim 1, further comprising meansfor connecting said apex terminals to a three-phase a.c. power supplyfor driving the elevator at a high speed.
 10. In an elevator drivingsystem in which the elevator is driven by a three-phase induction motorat different speeds, and a control system is provided for the motor, theimprovement comprising the three-phase induction motor havingdelta-connected armature windings, apex terminals for thedelta-cconnection and intermediate terminals for the respective phasewindings, the control system for the motor including means forconnecting said apex terminals to one another and for simultaneouslyconnecting said intermediate terminals to a three-phase a.c. powersupply for drIving the elevator at a high speed, and means fordisconnecting the mutual connection of said apex terminals and forsimultaneously applying a d.c. voltage across two terminals selectedfrom at least one of said apex terminals and said intermediate terminalsfor braking the elevator.
 11. In an elevator driving system according toclaim 10, the control system further including means for connecting saidapex terminals to a three-phase a.c. power supply for driving theelevator at a low speed.
 12. A method for driving an elevator in which athree-phase induction motor having delta-connected armature windings,apex terminals of the delta-connection and intermediate terminals of therespective phase windings is provided, the method comprising the stepsof connecting the apex terminals to one another and simultaneouslyconnecting the intermediate terminals to a three-phase a.c. power supplyfor driving the elevator at a high speed, and disconnecting the mutualconnection of the apex terminals and simultaneously applying a d.c.voltage across two terminals selected from at least one of the apexterminals and the intermediate terminals for braking operation of theelevator.
 13. A method according to claim 12, wherein the step ofdisconnecting and applying a d.c. voltage includes applying the voltageacross two terminals selected from the apex terminals or brakingoperation of the elevator.
 14. A method according to claim 12, whereinthe step of disconnecting and applying a d.c. voltage includes applyingthe voltage across two terminals selected from the intermediateterminals for braking operation of the elevator.
 15. A method accordingto claim 12, wherein the step of disconnecting and applying a d.c.voltage includes applying the voltage between an arbitrarily selectedapex terminal and an intermediate terminal of the phase winding oppositeto the selected apex terminal for braking operation of the elevator. 16.A method according to claim 12, wherein the step of disconnecting andapplying a d.c. voltage includes applying the voltage via a controlledrectifier circuit having a plurality of thyristors and connected an ana.c. power supply.
 17. A method according to claim 16, furthercomprising the steps of generating a speed instruction signal duringbraking operation of the elevator, detecting the rotating speed of theinduction motor, comparing the speed instruction signal with thedetected speed of the induction motor, and controlling the thyristors inresponse to the result of the comparison.
 18. A method according toclaim 17, further comprising the steps of detecting the physicalposition of the elevator car and controlling the generation of the speedinstruction signal in accordance with the detected position of theelevator car.